﻿414 
  N. 
  STORY-MASKEXYNE 
  AND 
  W. 
  FLIGHT 
  ON 
  THE 
  CHARACTER 
  

  

  The 
  oxygen 
  ratios 
  correspond 
  very 
  nearly, 
  it 
  will 
  be 
  observed, 
  

   with 
  the 
  formula 
  2(RO 
  Si0 
  2 
  )H 
  2 
  0, 
  or 
  that 
  of 
  a 
  bronzite, 
  two 
  equiva- 
  

   lents 
  of 
  which 
  are 
  combined 
  with 
  one 
  equivalent 
  of 
  water. 
  

  

  The 
  darker 
  matrix 
  could 
  not 
  be 
  separated 
  from 
  the 
  above 
  mineral, 
  

   which, 
  as 
  has 
  been 
  stated, 
  filled 
  very 
  small 
  cavities 
  in 
  many 
  parts 
  ; 
  

   nor 
  could 
  all 
  the 
  vaalite 
  be 
  removed. 
  The 
  specimen 
  employed 
  for 
  

   analysis, 
  which 
  was 
  more 
  or 
  less 
  mixed 
  with 
  these 
  substances, 
  had 
  

   the 
  following 
  composition 
  : 
  — 
  

  

  Silicic 
  acid 
  39-732 
  

  

  Alumina 
  . 
  2-309 
  

  

  Iron 
  protoxide 
  J 
  . 
  . 
  9-690 
  

  

  Magnesia 
  24-419 
  

  

  lime 
  10-162 
  

  

  Carbonic 
  acid 
  6-556 
  

  

  Water 
  7-547 
  

  

  100-415 
  

  

  It 
  may 
  be 
  assumed 
  that 
  the 
  lime 
  and 
  carbonic 
  acid 
  are 
  present 
  as 
  

   carbonate 
  of 
  lime, 
  which 
  is 
  distinctly 
  recognizable 
  under 
  the 
  micro- 
  

   scope. 
  A 
  small 
  amount 
  of 
  alumina 
  invariably 
  accompanies 
  bronzite, 
  

   whether 
  as 
  unchanged 
  crystal 
  or 
  in 
  the 
  hydrated 
  form 
  ; 
  so 
  that 
  it 
  is 
  

   difficult 
  to 
  base 
  calculations 
  as 
  to 
  the 
  amount 
  of 
  vaalite 
  present 
  on 
  

   the 
  amount 
  of 
  this 
  oxide. 
  If, 
  however, 
  we 
  regard 
  the 
  whole 
  of 
  the 
  

   alumina 
  as 
  present 
  in 
  the 
  form 
  of 
  that 
  mineral 
  and 
  assume 
  that 
  the 
  

   excess 
  thus 
  taken 
  compensates 
  for 
  the 
  iron 
  oxide 
  which 
  must 
  neces- 
  

   sarily 
  accompany 
  it, 
  we 
  obtain, 
  after 
  subtracting 
  the 
  oxygen 
  ratios 
  

   of 
  the 
  constituents 
  of 
  vaalite, 
  the 
  following 
  residual 
  oxygen 
  ratios 
  

   given 
  in 
  column 
  I. 
  : 
  — 
  

  

  I. 
  II. 
  

  

  Silicic 
  acid 
  17-610 
  17-6 
  

  

  Protoxide 
  9-769 
  9-6 
  

  

  Water 
  5-265 
  5-2 
  

  

  In 
  column 
  II. 
  of 
  the 
  above 
  Table 
  are 
  given 
  the 
  oxygen 
  ratios 
  

   of 
  a 
  mixture 
  of 
  nine 
  equivalents 
  of 
  the 
  hydrated 
  bronzite 
  and 
  two 
  

   equivalents 
  of 
  serpentine, 
  of 
  which 
  mixture 
  it 
  is 
  assumed 
  the 
  matrix 
  

   of 
  this 
  rock 
  consists. 
  

  

  Among 
  the 
  minerals 
  thus 
  incompletely 
  decomposed 
  in 
  the 
  rocks 
  of 
  

   New 
  Rush, 
  beside 
  the 
  hydrated 
  bronzite 
  already 
  described, 
  there 
  

   exists, 
  in 
  considerable 
  quantities, 
  a 
  fibrous 
  transparent 
  mineral, 
  ir- 
  

   regular 
  in 
  its 
  outline, 
  but 
  exhibiting 
  an 
  augitic 
  cleavage, 
  of 
  a 
  pale 
  

   brownish 
  colour, 
  possessing 
  in 
  some 
  lights 
  a 
  violet 
  tinge. 
  

  

  Between 
  the 
  fibres 
  of 
  this 
  mineral 
  there 
  are 
  occasionally 
  seen 
  

   minute 
  bars 
  of 
  the 
  brown 
  vaalite 
  ; 
  but 
  it 
  seems 
  tolerably 
  free 
  from 
  

   calcite. 
  This 
  variety 
  of 
  vermiculite 
  is 
  occasionally 
  associated 
  with 
  

   a 
  yellow 
  wax-like 
  substance, 
  which 
  is 
  probably 
  opal. 
  The 
  mineral 
  

   of 
  which 
  we 
  are 
  speaking 
  is 
  one 
  that 
  was 
  described 
  by 
  one 
  of 
  us 
  at 
  

   the 
  reading 
  of 
  Mr. 
  Dunn's 
  paper, 
  from 
  its 
  microscopic 
  and 
  optical 
  

   characters, 
  as 
  enstatite. 
  It 
  is 
  in 
  fact 
  a 
  ferriferous 
  enstatite 
  or 
  

  

  